Can the natural man understand the things of God?
No. The natural man is only body and soul, spiritually dead, and cannot comprehend the things of God. Scripture says he does not receive them, they are foolishness to him, and he cannot know them because they are spiritually discerned. Understanding requires spiritual discernment, not human wisdom.
Les explains that 1 Corinthians 2:13-14 contrasts human wisdom with the Holy Spirit's teaching. The natural man, who is only body and soul, is spiritually dead; therefore he cannot comprehend the things of God. Paul writes that the natural man does not receive the things of the Spirit of God because they are foolishness to him, and neither can he know them, because they are spiritually discerned. Les notes that when unbelievers are in his class, he tells them plainly that if they do not know the Lord, they will not understand everything he teaches; it will go over their heads. But when a person becomes a believer, what was previously unclear becomes visible, and they can see the whole thing and question nothing.
But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned.